This invention relates to steering systems and methods for a train of vehicles, such as a train of mobile conveyor machines.
Belt conveyors are well known and are efficient means for moving large quantities of materials such as ore, coal and granular stone over a predetermined distance extending either horizontally, vertically or both. One form of conveyor system known for mining applications is a system involving a series of conveyors mounted on wheels so as to make the system easily movable. Because of the manner in which mines are developed and extended, it may be necessary for a relatively long conveyor system to be moved along a substantially curved or zig zag course. Under such circumstances, it can be difficult and time consuming to move the conveyor system when required. It will also be appreciated that it may be necessary to move the conveyor system and to make adjustments to the system fairly frequently as the mining machine advances in a mine.
U.S. Pat. No. 5,366,059 issued Nov. 22, 1994 to Prairie Machine & Parts Mfg. Ltd. describes and illustrates a conveyor system comprising a plurality of conveyor vehicles connected together in the form of a train and also describes a steering system for steering this train of vehicles. All but one of the vehicles in the train has a single pair of steerable wheels with the vehicle at the outby end of the train (that is the end to which the mined material is being delivered) having two pairs of steerable wheels. Hydraulic cylinders are used to steer each of the pairs of steerable wheels and there is a control mechanism for controlling and coordinating these cylinders in order to set the steering angles of the pairs of wheels.
The aforementioned known steering system uses a control system that has sensors for determining the current steering angle for a selected pair of wheels and generating an electrical signal indicative thereof and an electronic memory for storing a series of these electrical signals as the train is travelling. There is also a mechanism for determining the distance the wheels on the train have been travelling. The control system sets the steering angle for each pair of wheels other than the selected pair at substantially the same steering angle that the selected pair had when they were at the location where the respective further pair is located.
One difficulty with this known system is that all of the axles in the train except for first and last axles must be pivotally connected to adjoining vehicles by front and rear pivot devices, each providing a vertical pivot axis. The front pivot device is located forwardly of its respective axle and the rear pivot device is located rearwardly of its respective axle. Furthermore, this steering system requires a mechanism for locking each of the axles (except for the first and last axles) in a position at a right angle to the longitudinal centre line of either the vehicle immediately in front of the respective axle or the vehicle immediately to the rear thereof. Needless to say, this type of pivoting axle system adds substantially to the cost of these conveyor vehicles. Moreover, although it is desirable to provide a conveyor vehicle system which does not require a high mine ceiling in which to operate, this known steering system which requires the use of a series of axles on which to mount the wheels is not particularly desirable from the standpoint of reducing the height of the conveyor system.
There is a need in the mobile belt conveyor industry to provide an improved train of conveyor vehicles which can be easily and reliably steered automatically by an operator, for example an operator located at the leading end of the train of vehicles who is steering a leading set of wheels, that is the pair of wheels at the end of the train towards which the train is moving.
In addition, there is a perceived need to provide a steering system that can be used to steer a plurality of vehicles arranged end-to-end in a train, this train of conveyors being suitable for use in low mining seams, and in particular a steering system for such a train of vehicles that can be used without the need to mount each pair of wheels on a single axle that can be pivoted about a vertical pivot axis.